We propose a systematic quantitative study of vertical and horizontal eye movement in normal human subjects and patients to better understand the physiology and patho-physiology of vertical ocular motor control in man. Numerous studies have documented differences in the anatomy and physiology of vertical and horizontal ocular motor control in several animal species. These observations must be tested in human subjects because of the possible existence of significant species differences. The paucity of quantitative studies of vertical eye movements in the clinical literature can be directly traced to the difficulty in precisely recording vertical eye movements. We plan to carefully assess the advantages and disadvantages of 3 different techniques for recording vertical eye movements (electro-oculography, photoelectric and scleral search coil). We will use precise stimuli and digital computer analyses techniques to study saccadic, pursuit, optokinetic, vestibular and visual-vestibular eye movements. Normative data will be established for each type of eye movement and differences between the characteristics of vertical and horizontal eye movements will be identified. We will study patients with focal lesions in areas known to be critical for generating vertical eye movements (e.g., the mesencephalic reticular formation) and patients with syndromes known to affect vertical ocular motor control (e.g., progressive supranuclear palsy). Eye movement recording devices will be selected for each patient based on the type of test, the patient's ability to cooperate, specific questions being asked and our experience gained from testing prior subjects. The immediate, pragmatic objective of the proposed research is to improve the diagnostic value of clinical eye movement tests, resulting in earlier and more accurate localization of central nervous system lesions. The long-term objective is to understand how the human brain controls vertical eye movements.